I'm not disputing that this kind of attack is totally unfair. I'm just saying that a professional wizard who knows how to use magic to kill and has been given time to prepare will flatten just about anyone. They don't even need a sympathetic link to you to do it - they can target your general area and simply swing around enough power that you become collateral damage if they do it right.
Classic example is Ebenezar's "meteor" strike. This is how he probably did it;
He knew the location of Ortega's fortress and that Ortega had holed up there. So what does he do? He digs up some old observations done over months of amateur astronomy work of a certain satellite's orbit and its specifics; those are some of the aspects he needs, prepared ages ahead of time. Add the satellite itself as an aspect, its own kinetic energy and the dynamic energy of its orbit - those are scholarship declarations BTW - and you got a decent beginning. Having previously named the satellite himself along with Harry and having good photos of it, he has a permanent sympathetic link. So far, the groundwork only needed a couple of hours if you discount the original time spent doing observations. (this BTW is why many old wizards are always doing research, preparation and experiments - so they already have some stuff when they need a quick spell).
Now, we go to the actual casting. Ebenezar starts casting spells on the sat, minor pushes and pulls at his minimum thaumaturgy complexity. That being 6 shifts, he uses those minor spells to create more aspects like "added momentum", "stabilizing spin", "good re-entry angle", "minimum-friction trajectory", "high-speed final approach", "perfect aim" and anything else he can think of to give the satellite to enhance its lethality on an impact via aspects.
Finally, as the sat interrupts its orbit and begins said final approach, he actually casts his spell. The shifts he's gathered are 6 base for his minimum complexity, +4 spell focus/specialization, the "clarity of purpose, absolute conviction" aspects via conviction declarations for +4, the "iron self-control, focused will" aspects via discipline declarations for +4, the "perfectly-aligned circle, esoteric incantation" aspects via Lore declarations for +4, +4 for the satellite's true name and for the name he and harry gave it themselves, +6 for the satellite's high mass, original speed and attitude coming from scholarship assessments, +10 for 5 more assessments from previous astronomic observations, +14 to +20 for the 7-10 aspects he created on the sat itself, +12 for two mild consequences he gives over 3 different scenes with rest intervals to recover between them (the spell took a day to prepare at least so a lot of scenes) for a grand total of seventy-four shifts of power.
74 shifts means that the actual casting for the spell will take him a maximum of 25 exchanges if he goes with entirely safe power control; he has a total control of 7 and thus can control 3 power/exchange with perfect safety. The Wards and other protections in his own house ensure that he gets those exchanges unless something major happens.
Let's go with the actual spell. 74 shifts is barely twice that of the heart-ripping spell a two-bit sorcerer can manage but the results are rather more spectacular. Ebenezar will double-park his russian sat on Ortega's manor with extreme prejudice. 10 entire zones of space will be needed for the double-parking so that's 20 shifts. Also, the 10-ton sat is being parked at a bit over 20 kilometers/second courtesy of all that prodding and directed reentry - so the spell's effect is 54 shifts strong.
54 shifts means the walls and doors and roof of the manor are so much dust, fortified or otherwise (12 shifts takes down vault doors). It also means that anyone in the manor is also vaporized - they can't hope to evade the hit or absorb the stress. And because the spell is a big kinetic strike rather than direct magical energy, thresholds, circles, running water and other protections from magic are irrelevant.
And that was that for Ortega, his manor, his vampire flunkies, his soldiers, his servants, their servants, his food, their food, his dogs, their dogs, the cats and mice and everyone and everything else in the area. For effectively one day's worth of preparation for a powerful wizard who had neither the sympathetic links to them nor directed any magical energy they could detect their way at all - but a wizard who could do a professional killing spell (not a half-@$$ed entropy or heart-ripping curse), and happened to know their location at the time. Tunguska and Krakatoa were probably at least an order of magnitude bigger than that and were still done by the same single powerful wizard and enough research and preparation.
Serious destructive magic cannot be defended against directly. You either need to sit against powerful permanent Wards or you need to deny the wizard his target. That usually is thought to mean a sympathetic link but it could be as simple as his knowing where you'll be at a certain time well enough in advance to lever the power required.